This section provides background information related to the present disclosure which is not necessarily prior art.
FIG. 1 is a view showing an example of a conventional III-nitride semiconductor light-emitting device. The III-nitride semiconductor light-emitting device includes a substrate 10 (e.g., sapphire substrate), a buffer layer 20 grown on the substrate 10, an n-type III-nitride semiconductor layer 30 grown on the buffer layer 20, an active layer 40 grown on the n-type III-nitride semiconductor layer 30, a p-type III-nitride semiconductor layer 50 grown on the active layer 40, a current spreading electrode 60 formed on the p-type III-nitride semiconductor layer 50, a p-side pad electrode 70 formed on the current spreading electrode 60, an n-side pad electrode 80 formed on the n-type III-nitride semiconductor layer 30 exposed by mesa-etching the p-type III-nitride semiconductor layer 50 and the active layer 40, and a protective film 90.
The current spreading electrode 60 serves to allow current to be smoothly supplied to the entire p-type III-nitride semiconductor layer 50. The current spreading electrode 60 may be provided almost on the entire surface of the p-type III-nitride semiconductor layer 50 and formed as a light-transmitting conductive film using ITO or Ni and Au or as a reflective conductive film using Ag, for example.
The p-side pad electrode 70 and the n-side pad electrode 80, which are metal electrodes for current supply and external wire bonding, may be made of any one selected from the group consisting of, e.g., Ni, Au, Ag, Cr, Ti, Pt, Pd, Rh, Ir, Al, Sn, In, Ta, Cu, Co, Fe, Ru, Zr, W, and Mo, or a combination thereof.
The protective film 90, which is made of SiO2, can be omitted.
With the large area tendency and high power consumption of the semiconductor light-emitting device, a plurality of electrodes and branch electrodes have been introduced for smooth current spreading in the semiconductor light-emitting device. For example, as the III-nitride semiconductor light-emitting device gets larger (e.g., width×length=1000 μm×1000 μm), the p-side pad electrode 70 and the n-side pad electrode 80 are provided with a branch electrode to improve current spreading. Furthermore, a plurality of the p-side pad electrodes 70 and a plurality of the n-side pad electrodes 80 may be arranged, respectively, for sufficient current supply.
The electrode and the branch electrode, which are electrically connected to each other, are ideally equipotential. But, there is a tendency that current is actually concentrated on the center of the electrode to which current is being applied.
As in the above, when current is concentrated on a local region of the semiconductor light-emitting device, light cannot be uniformly emitted from the entire light emission area of the semiconductor light-emitting device, which degrades characteristics of the semiconductor light-emitting device in the long term.